Circle Circumference Calculator
Calculate the circumference of a circle from its radius or diameter. Get the formula, see each calculation step, and find the circle's area, radius, and diameter in your chosen unit.
Calculate circumference
Enter a positive radius or diameter. The calculator uses π for accurate results.
Circle circumference formula
The circumference is the distance around the edge of a circle. You can calculate it using either the radius or the diameter.
C = 2πr
When you know the diameter:
C = πd
In these formulas:
- C is the circumference.
- r is the radius, measured from the center to the circle's edge.
- d is the diameter, measured across the circle through its center.
- π (pi) is approximately 3.141592653589793.
Example calculation
Suppose a circle has a radius of 5 meters.
- Start with C = 2πr.
- Substitute the radius: C = 2 × π × 5.
- Calculate: C ≈ 31.4159 meters.
The diameter is 10 meters, and the area is approximately 78.5398 square meters.
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Frequently asked questions
What is the circumference of a circle?
The circumference is the distance around the outside edge of a circle. It is the circle equivalent of a perimeter.
What is the formula for circumference?
Use C = 2πr when the radius is known, or C = πd when the diameter is known. The constant π is approximately 3.141592653589793.
Can I calculate circumference from diameter?
Yes. Multiply the diameter by π. For example, a diameter of 10 meters gives a circumference of approximately 31.4159 meters.
What is the difference between circumference and area?
Circumference measures the distance around the circle in linear units. Area measures the space inside the circle in square units.